Interpretive Summary: Conservation tillage is used on over 40 percent of the 24 million cropland acres in the southeastern USA. Black oat and oilseed radish, major cover crops grown in Southern Brazil and Paraguay, could be used as alternatives to the traditional cover crops, crimson clover, and winter rye to help increase cropping system diversity and reduce the potential for disease and pest buildup. Researchers from the Southern Piedmont Conservation Research Unit, the University of Georgia, Instituto Agronômico do Paraná, and EMBRAPA Agrobiologia investigated the influence of these cover crops on N availability over four years at the J. Phil Campbell, Sr., Natural Resource Conservation Center, Watkinsville, GA. Black oat and oil seed radish produced similar amounts of biomass with similar amounts of N as crimson clover. Rye produced more biomass than the other cover crops but reduced N availability during the summer cropping season. Availability of released soil N following black oat and oil seed radish was similar to that following crimson clover. The greater availability of N following black oat and oilseed radish compared to rye indicates that no adjustments in N recommendations would be needed following these cover crops in conservation tillage systems and soils in the region. Producers can save on fertilizer costs compared to rye and reduce the potential for negative environmental impacts by using black oat or oilseed radish as cover crops.

Technical Abstract:
Winter cover crops are essential in conservation tillage systems to protect soils from erosion and for improving soil productivity. Black oat (Avena strigosa Schreb) and oilseed radish (Raphanus sativus L.) could be useful cover crops in the Southeastern USA but successful adoption requires understanding their influence on N availability in conservation tillage systems. Black oat and oilseed radish were compared to crimson clover (Trifolium incarnatum L.), and rye (Secale cereale L.) for biomass production and effects on N mineralization during the summer crop growing season from fall 1998 through summer 2002 near Watkinsville, GA. Rye produced 40 to 60% more biomass while N contents were less than the other cover crops. Oilseed radish and black oat N contents were similar to crimson cover. Black oat, oilseed radish and crimson clover C:N ratios were less than 30 while rye averaged 39. Amount of N mineralized in 90 days (Nmin90) measured with in situ soil cores was 1.3 to 2.2 times greater following black oat, crimson clover, and oilseed radish than following rye. No differences in Nmin90 were found between black oats, crimson clover, and oilseed radish in 1999 and 2000. The amount of potentially mineralizable N (N0) was not different due to cover crop but was 1.5 times greater in 2000 and 2002 than in 1999. The rate of N mineralization (k) was 20 to 50% slower following rye than the other three cover crops. Black oat and oilseed radish biomass production and soil N mineralization dynamics were more similar to crimson clover than to rye which indicates that they could be used as cover crops in the southeast without significant changes in N recommendations for most crops.